In H.264, which is an international standard for picture coding, intra-frame predictive coding is performed in order to improve a compression rate in coding using correlation of pixels between blocks (see Non-Patent Document 1). This intra-frame prediction is performed in units of blocks in which some pixels are collected, and three types of block sizes of 4×4, 8×8, and 16×16 are available to a luminance signal. Furthermore, a plurality of prediction modes are selectable for each block size.
This H.264 uses a method based on extrapolation prediction at the time of intra-frame prediction, but there is a problem in that prediction efficiency thereof is low. In order to solve this problem, suppression of block distortion using a deblocking filter for an entire frame is performed and thus the computational complexity increases.
Furthermore, technology described in Non-Patent Document 2 is known as a scheme for improving coding efficiency in intra-frame prediction. This technology is a scheme for searching an encoded area for a block having a smaller error with respect to an encoding target block in the intra-frame prediction and performing encoding using a prediction error thereof.
FIG. 18 is a flowchart illustrating an example of an intra-frame predictive encoding process in accordance with conventional technology. In intra-frame predictive encoding of Non-Patent Document 2, first, an encoding target picture is divided into N blocks 1 to N having the same size (step S301). Then, the intra-frame predictive encoding is performed on the first block 1 (step S302). Subsequently, in encoding of block 2 and subsequent blocks, inter-frame predictive encoding is performed using a block having a smaller prediction error in an encoded area as a reference picture and information on a motion vector to the reference picture and a prediction error are encoded (step S303). This process of step S303 is repeated up to the last block N.